The present invention relates to a radial piston machine, e.g., a radial piston pump or a radial piston engine.
The starting point of the present invention is a machine having a cylinder housing which has multiple radially positioned cylinder bores. A radially displaceable piston, which is centrally supported on an eccentric rotatable relative to the cylinder housing, is located in each cylinder bore. The cylinder housing may be stationary and the eccentric is rotatable. However, the reverse construction is also possible. In most cases, this is therefore a radial piston pump having a stationary cylinder housing and having a rotatable eccentric which is coupled to a component which rotates in operation to drive the pump.
A radial piston pump has the advantage, contingent on its operating principle, that the delivery flow is limited by the intake stroke restriction to an average rotational speed of, for example, 1600 rpm. Above this speed, the piston interior is no longer fully filled. This means that the beginning of delivery is dependent on the filling after the piston has closed its associated suction hole. Upon the beginning of delivery, the piston strikes the enclosed oil column with a velocity dependent on the rotational speed, and pumps the oil out into a collecting channel connected with the user via a non-return valve, implemented as a peripheral leaf spring, which closes all outlet bores of the piston. Since the piston does not begin delivery at zero velocity, a strong pressure surge arises in the piston interior. The pressure peak generated by such a pressure surge exceeds several times the outlet pressure in the collecting channel. Contingent on this principle, the pressure surges are amplified with increasing rotational speed. The pressure surges of all the pistons induce a structure-borne sound which is emitted via the housing wall as airborne sound.
As described in German Published Patent Application No. 43 36 673, an attempt has been made to reduce the pressure peaks caused by the described pressure surges and thus to make the radial piston machine less noisy. In this case, a radially acting attenuator (implemented as a xe2x80x9ccirclipxe2x80x9d or xe2x80x9cwaved spring,xe2x80x9d e.g., a polygonal circlip) is provided. This circlip is inserted between two sliding rings which are located between the foot of the piston and the eccentric. This attempted solution does lead to a significant noise reduction. However, there is the disadvantage that the external sliding ring is sometimes highly stressed by bending. Due to this, its service life is insufficient.
It is therefore an object of the present invention to provide a radial piston machine (e.g., a radial piston pump) in which two requirements are met simultaneously, namely the best possible noise reduction during operation of the machine and the least possible stress on the individual components, so that a long service life and/or longer operation without malfunctions may be ensured.
The above and other beneficial objects of the present invention are achieved by providing a radial piston machine as described herein. According to one example embodiment of the present invention, the stiffness of the circlip is reduced by providing a material weakening along its middle axis. The concept of xe2x80x9cmiddle axisxe2x80x9d does not mean axis of rotation of the eccentric but the center line extending halfway along the width of the circlip around the circumference. This line is in the plane of the piston axis.
The effect of the measure previously described is that the elastic flexibility of those parts of the circlip which reinforce the external sliding ring is increased. When a strong pressure surge arises in one of the piston interiors, the external sliding ring is deformed as before to decrease the pressure surge. However, according to the present invention, the circlip is also deformed to a greater extent than before. The external sliding ring and the circlip are more uniformly stressed by bending than previously, so that overloading of the external sliding ring is avoided without the danger of overloading the circlip. The desired reduction of noise generation is achieved simultaneously, and at least to the same extent as before.
Theoretically, it is possible to increase the elastic flexibility of the circlip by reducing its thickness. However, this is difficult because commercial raw material is not available in the necessary fine thicknesses. A reduction of the thickness by mechanical processing is also not satisfactory due to higher costs. Thus, the provision of a material weakening along the area of the central axis of the circlip according to the present inventionxe2x80x94while maintaining a commercial material thicknessxe2x80x94is a particularly cost-effective method to achieve increase of the flexibility.
There are numerous possibilities for obtaining the respective optimum degree of flexibility of the circlip by selection of the shape and size of the material weakeningxe2x80x94as well as by its positioning along the central axis of the circlip. However, experiments are necessary for optimization.
The present invention is applicable for numerous configurations of radial piston machines, e.g., for radial piston pumps having a stationary cylinder housing and a rotatable eccentric. The circlip may include an open ring, the ring ends of which form a gap. Because of this, the circlip has increased flexibility. It may xe2x80x9cbreathe.xe2x80x9d However, the use of a circlip which is closed is also possible. A requirement for the use of an open circlip is, however, that its thickness be sufficiently great so that overlapping of the ring ends is reliably avoided under stress. This is a further aspect which argues against the reduction of the thickness of the circlip as described above.
The width of the circlip from the conventional configuration may be maintained. Thus, it may be ensured that the circlip is securely guided between other components, in the direction of the rotational axis of the eccentric, e.g., between two axial disks. In addition, it is ensured that deformations of the annular spring occurring in operation occur symmetrically to the plane of the piston axis, exactly as is the case of the external sliding ring (and possibly, if present, in the internal sliding ring).
In a further example embodiment of the present invention, an inner sliding ring may be provided between the eccentric and circlip, as described in German Published Patent Application No. 43 36 673. In this manner, during operation the speed of rotation of the internal circlip is at most slightly less than the speed of rotation of the eccentric. Speeds of rotation which are reduced even further will result for the circlip and for the external sliding ring. As a result, the sliding speed of the external sliding ring on the foot of the piston is therefore relatively low. The sliding speed of the internal sliding ring on the eccentric is also rather low. In this manner, very low wear is produced both at the foot of the piston and on the outer face of the eccentric.
The eccentric is, generally, a massive component. Nonetheless if it is necessary to reduce even further the noise arising during operation of the radial piston machine, a flexible eccentric may be provided.
The present invention is described in more detail in the following description with reference to example embodiments which are illustrated in the Figures.